Along with the recent widespread use of cordless equipment such as personal computers and mobile phones, there is an increasing demand for miniaturization and higher capacity of a secondary battery that functions as a power supply for such equipment. An example of batteries satisfying the demand includes an air battery. The air battery utilizes oxygen in the air as an active material for a positive electrode, and allows most of the volume thereof to be used for a negative electrode. Therefore, the air battery is considered to be preferable for increasing the density of energy.
JP 5(1993)-242906 A and JP 5(1993)-275108 A have proposed batteries using an air electrode as a positive electrode, a hydrogen-absorbing alloy as a working material for a negative electrode, and an ion-exchange film as an electrolyte. In such batteries, the filling volume of a negative electrode can be increased compared with a conventional nickel-metal hydride battery, so that higher capacity is expected.
However, in the case where a cation-exchange resin is used as an electrolyte, protons function as ion conductors, which puts the entire cation-exchange resin in an acidic atmosphere. As a result, a hydrogen-absorbing alloy may be corroded at a site where the cation-exchange resin comes into contact with the hydrogen-absorbing alloy. On the other hand, in the case where an anion-exchange resin is used as an electrolyte, it is required to keep a path for conducting ions up to the inside of a negative electrode so that the entire hydrogen-absorbing alloy can participate in a reaction.
In order to eliminate the influence of carbon dioxide in the air, JP 5(1993)-275108 A recommends using a cation-exchange film as an electrolyte to be disposed between a positive electrode and a negative electrode, and discloses that an ion-exchange resin is allowed to be present in a hydrogen-absorbing alloy layer of a negative electrode. However, JP 5(1993)-275108 A merely describes an example in which a negative electrode is impregnated with a liquid cation-exchange resin, and does not consider the problem of corrosion of a hydrogen-absorbing alloy. Furthermore, JP 5(1993)-275108 A does not describe what kind of anion-exchange resin can be used in the case where an anion-exchange resin is used as an ion-exchange resin of the hydrogen-absorbing alloy layer. Even if general anion-exchange resin powder is dispersed together with a hydrogen-absorbing alloy, and allowed to be present in the hydrogen-absorbing alloy layer, it is difficult for ions to move between the anion-exchange resin powders and between the hydrogen-absorbing alloy and the anion-exchange resin, which makes it difficult to use the entire hydrogen-absorbing alloy for a charging/discharging reaction.
Furthermore, in JP 5(1993)-242906 A, an alkaline electrolyte is used for keeping a path for conducting ions in a negative electrode, which causes a safety problem such as leakage in an unsealed air electrode. Furthermore, as in a nickel-metal hydride battery, the problem of corrosion of a hydrogen-absorbing alloy caused by an alkaline electrolyte is not solved. Furthermore, in JP 5(1993)-242906 A, mechanical charging that uses filling of hydrogen gas is adopted instead of electrical charging, which may cause trouble in operability of a user.
Therefore, the present invention overcomes the above-mentioned problem in the prior art, and its object is to provide an air-hydrogen battery with high energy density capable of preventing corrosion of a hydrogen-absorbing alloy and improving the utilization factor of the hydrogen-absorbing alloy in a charging/discharging reaction.